Why was this sentence considered wrong?

Hola K, quizás sea mejor poner 'por mí' al lado del participio, "resolved by me".  A lo mejor se puede escribirlo de otra (su) manera, y no es incorrecto, pero tiene un énfasis diferente "resolved in two minutes... oh by the way, it was by me".  Lo adivino!  Un saludo, Robin. 

Hi Robin,

Thanks, that’s helpful. 

I guess that my concern is that, at times,  answers are marked incorrect for things that are not related to the lesson or the question. 

K